I really need a refresh rate of 75 or higher? Did I just buy an expensive paperweight?

Return it and get your money back.

Most computer screens and computers only use the 60 Hz display refresh rate.

This is the common standard and there is no way to change this, at all.

There is no getting around this.

All Apple computers use the 60 Hz display refresh standard.

Sorry.

If you know of any other computers that have a computer display or use an external monitor with a display refresh rate greater than 60 Hz, sell that iMac and use a different computer that supoorts what you need for your physical condition/impairment

Most iPads, other than the newest 2nd and 3rd gen iPad Pro models use a screen with a 120 Hz screen refresh rate.

These do not, as yet, exist for Macs.

Obviously, Apple does not offer any display refresh frequency rate options for you.

Have you tried just simply turning down the screen brightness?

Change the default display resolution and move the display farther away from your eyes?

Change the color temperature from cool to a warmer color temperature?

There are things you can do to a computer display to minimise eye fatigue and causing migraines.

If you purchased directly from Apple within the last 15 days you can return it for any reason.

I received your response.

I have been using Macs since the mid-1990’s and all displays available for Macs have always been 60 Hz refresh rates.

I owned and used a PowerMac G3 beige desktop Mac fully loaded for 8 years with both old cathode ray monitors and flat LCD screen monitors that I ported over to my 2003 PowerMac G4 that I used for another 8 years before moving on to an all-in-one iMac.

All of these computer screens were 60 Hz refresh rate.

You can set Mac compatible computer screens for different pixel resolutions, but the 60 Hz refersh rate remains the same.

CRTs running at lower refresh rates can generate annoying flicker, especially in peripheral vision, and at high brightness.

A dot on the screen get bright when hit by the electron beam, then fades until the next refresh.

Modern iMacs have LCD screens, which do not flicker, even at low refresh rates. The backlight is on continuously and the liquid crystal and polarizing layers determine which dots allow light to pass through. If light is coming through a dot, its brightness does not change with the refresh rate. A low refresh rate may make moving objects jerky, but does cause flicker.